As Atmospheric River Reaches California, Scripps and NOAA Researchers Take Flight to Observe It

Precipitation due to a series of strong atmospheric rivers could provide partial relief to drought-stricken West

Researchers from Scripps Institution of Oceanography, UC San Diego, and NOAA are taking part in research flights to observe this distinctive type of storm system that has historically provided significant precipitation to California.

Scientists tracked the evolution of an “atmospheric river,” a narrow corridor of strong water vapor transport that can extend thousands of miles, as it made landfall in central California late last week. Atmospheric rivers can provide beneficial water supply and snowpack to the West Coast as well as create conditions for dangerous floods that affect lives and property. NOAA, Scripps, USGS and other agency/institution researchers, working with water managers for the state, Sonoma County and elsewhere, are studying them with the goal of providing better information for earlier and more accurate extreme weather forecasts. Scripps and USGS scientists are also looking at how atmospheric rivers may serve as “drought busters” and how climate change may affect atmospheric rivers in future decades.

Scripps researchers said that the pattern expected to reach California during the Feb. 8 weekend had the potential to provide some relief, but would likely not reverse the dangerous drought conditions throughout California and the West that have built up over the last three years.

“Part of the reason for the drought has been the absence of atmospheric river storms hitting the region over the last year. The next several days could help change that, as a series of modest strength atmospheric rivers hit northern California. It is likely that over the next week these storms will produce as much precipitation in northern California as has fallen in the last four months. It could even triple the amount to date.”, said Marty Ralph.

Ralph heads a new center devoted to California’s special precipitation characteristics that has been established at Scripps Institution of Oceanography, UC San Diego. At the core of the Center for Western Water and Weather Extremes (CW3E) will be use of a unique advanced network of monitoring stations throughout the state to help industries and 38 million California residents understand phenomena that affect the economy and everyday life in myriad ways.

The network, built over the last 5 years by NOAA and Scripps through support from California’s Department of Water Resources will initially contain four atmospheric river observatories, monitoring stations located in northern and central California that measure amounts of water vapor in the atmosphere and other climate variables.

For this event, Ralph and colleagues gathered data aboard a NOAA Gulfstream IV aircraft that began flying over the Pacific Ocean off the U.S. West Coast on Feb. 7. During the flights, researchers measured air pressure, temperature, humidity, wind speed and direction to help better understand atmospheric rivers.

Aboard the aircraft, researchers released small parachuted devices, called dropsondes, across the atmospheric river over the Pacific Ocean. The dropsondes measure atmospheric conditions, such as pressure, temperature, humidity, wind speed and direction, and transmit the information back to the aircraft where a flight scientist uses it to guide the mission. After the dropsonde data is analyzed and processed, the information will be put into a standard format established by the World Meteorological Organization and provided to NOAA’s National Hurricane Center for inclusion in global and local-scale weather prediction models.

Mike Dettinger, a CW3E team member and research hydrologist with Scripps and the U.S. Geological Survey, noted that atmospheric rivers are behind many of the pivotal precipitation events in California, including 80 percent of the floodplain inundations along parts of the Central Valley where those inundations are a necessary part of ecosystem food webs and fish nurseries.

“Thus, better understanding of how atmospheric rivers work and how they may change in the future is critical to better water, floods, and ecosystem management and to plans for adapting to future climate changes,” he said.

Results from this study will help guide atmospheric river research for the upcoming CalWater 2 experiment, which begins in 2015 and will use land-based stations and a research ship as well as multiple aircraft.